Nervous Tissue - Histopathology

the nervous system is

an arrangment of neurons and their supporting tissue

how is the nervous system divided into

anatomically

1. central nervous system (CNS)

2. peripherial nervous system (PNS)

functionally

1. sensory division (afferent)

2. motor division (efferent)

the motor division is futher divided into

1. somatic nervous system

2. autonomic nervous system (ANS)

somatic system is part of

motor division - efferent - input

visceral system is part of

sensory division - afferent - output

what does the PNS system do for the CNS

conducts impulses to sensory and from motor to the CNS

autonomic nervous system (ANS) is composed of

preganglionic neurons in the CNS and postganglionic neurons in the ganglion

how is the ANS divided

1. parasympathetic

2. sympathetic

parasympathetic

maintains normal body homeostasis with its ganglia in or near effector organs

sympathetic

controls the body’s responses during emergencies and excitement, ganglia are close to the CNS

somatic is

consicously controlled or percieved

visceral is

not perceived consciously

what is the basic sturutres that neurons have?

1. large body cell body (perikaryon or soma)

2. a single axon

3. one or more dendrites

perikaryon

the nucleous surrounded by cytoplasm containing most of the cell’s organelles

axon

a single long process ending at synapses specialized in generating and conducting nerve impluses to other cells and also receive signals to modify their response

dendrites

elongated processes extending from the perikaryon and specialize in receiving stimuli from other neurons at their synapses

how any axonal endings does a single Purkinje cell have?

200,000

how are the neurons classified into?

1. multipolar neurons

2. bipolar neurons

3. unipolar or pseudo-unipolar neurons

4. anaxomic neurons

multipolar neurons

most common

one axon

two or more dendrites

bipolar neurons

one dendrite

one axon

make up sensory neurons of the retina, olfactory epithelium, and inner ear

unipolar neurons

single process that bifurcates close the perikaryon and include all sensory neurons excpet those that are bipolar

the longer end of the bifurcated process (unipolar) extends towards

the peripheral

the shorter end of the bifurcated process (unipolar) extends towards

CNS

anaxonic neurons

many dentrites

no true axon

regulate electrical changes of adjacent CNS neurons

what does the cytoplasm of the perikaryton contain?

numerous free polyribosomes and highly developed rough ER (basophilic) and are distinguished by Nissl bodies

Nissl bodies can be found

cell body and dendrites

golgi apparatus is only seen in ____, while mitochondria can be seen

cell body, throughout the neuron and abundant in the axon terminals

where do axons orginate from

axon hillock - pyramid shaped region of the perikaryon

axolemma

plasma membrane of the axon

axoplasm

axon cytoplasm

how is the axon different from a dendrites

formed in the axon hillock, which lacks basophilic granules

how is a dendrites different from axons

contains Nissl bodies, which allows a more granular appearance

branch have an acute angles

what are the types of neuroglial cells

1. oligodendrocytes (CNS)

2. astrocyte (CNS)

3. ependymal cell (CNS)

4. microgolia (bone marrow) (CNS)

5. Schwaan cell (PNS)

6. satellite cells (PNS)

oligodendrocyte main functions

1. myelin production

2. electrical insulation

astrocytes main functions

1. structural and metabolic support of neurons at synapses

2. repair processes

ependymal cell functions

1. aid production and movement of CSF

microglia main functions

defense and immune related activities

Schwaan cells main functions

1. myelin production

2. electrical insulation

satellite cells main functions

structure and metabolic support for neuronal cell bodies

how does the oligodendrocyte wraps around the axon

form multiple, multi-layered myelin sheath around diffrent axons

where the is oligodendrocytes predominant

glial cell in white matter

how do the oligodendrocytes look like

small rounded cells with condensed nuclei and unstained cytoplasm

what can the oligodendrocytes do

allow faster action potential propagation along axons in the CNS

Schwaan cells are also known as

neurolemmocytes

what does Schwaan cells form

myelin sheaths of neurons in the PNS

how does the Schwaan cells attach to the axon

completely wraps around a single axon by laying down multiple layers of cell membrane

what does the Schwann cells have

nodes of Ranvier, which help increase the speed of neuron signaling

what can the oligodendrocytes do that the Schwaan cells can’t

jump from node to node because its not covered by plasma membrane

what does the Schwaan cells have that oligodendrocytes don’t

thicker myelin sheath, enlarged non-axonal domain

non-myelinated nerve fibers have

autonomic nerves and small pain fibers which have small diameter axons

non-myelinated nerve fibers small axons

enveloped by the cytoplasm of Schwaan cells or oligodendrocytes depending on their location

what is mesoaxon

where the Schwaan cell plasma membrane becomes apposed to itself

non-myelinated action potential is ___ than for myelinated nerves

slower

myelinated nerve fibers are

larger nerve axons that are wrapped in concentric layers of Schwaan cell or oligodendrocytes plasma membrane (myelin sheath)

steps of myelination

1. axon laying near Schwaan cell

2. axon invaginates Schwaan cell

3. mesaxon formed by futher invagination by the axon

4. mesaxon makes several turns around the axon and lipids are deposited between the layers forming a myelin sheath

astrocytes is a

star shaped glial cell unique to the CNS

what is a astrocyte

process proximal regions contain reinforced bundles of intermediate filaments made of glial fibrillary acid protein (GFAP)

what is the most numerous type of glial cell in the brain

astrocytes

what other functions do astrocytes have

1. regulation of extracellular ionic concentrations around neurons

2. support of differentiating neurons during CNS development

3. use of process to associate with or cover synapses

4. use of fibrous processes with perivascular feet to cover capillary endothelial cells

5. forms a barrier layer lining the meninges at the external CNS surface

6. forms astrocytic scard to fill in space left by dead neurons

what does the use of processes in astrocytes do

affect synapse formation, function, and plascity

the use of fibrous processes in astrocytes does what

allow to modulate blood flow and move nutrients, waste, and other metabolites between neurons and capillarites

microglia is a major

mechanism of CNS immune defense

microglia are what type of cells

small cells with actively mobile processes, capable of moving though the CNS

where are microglia developed from

blood monocytes and are in the same family as macrophages

how does the microglia look like

nuclei appears denser and more elongated than glial cells

what type of diseases are associated with astrocytes

1. alzheimer’s

2. parkinson’s

3. huntington’s

4. motor neuron

5. multiple sclerosis

what type of disease are associated with microglia

1. alzheimer’s

2. parkinson’s

3. huntington’s

4. motor neuron

5. multiple sclerosis

6. frontotemporal dementia

astrocytes CNS functions

1. homeostasis

2. bbb maintaince

3. synaptic support

microglia CNS functions

1. homeostasis

2. phagocytosis

3. synaptic communication

4. synaptic pruning

5. surveillance

microglia are developed

from yolk sac

astrocytes are developed

from radial gila

ependymal cells are

columar or cuboidal cells that line ventricles of the brain and the central canal of the spinal cord

ependymal cells assist

in the production and circulation of cerebrospinal fluid (CSF)

ependymal cells also have ___ and they do not have ___

microvilli, basal lamina

ependymal cells are located in

interface between CSF and CNS parenchyma (helps in brain CSF barrier formation)

what helps maintain ependymal integrity and permeability and isolate harmful substance in CNS

tight junctions, gap junctions, and adhesion junctions between cells

what are they type of disease assciated with ependymal cells

1. neurotrauma

2. neurodegenerative disease

3. cerebrovascular disease

4. central nervous system infection

what is a result of agining in the ependymal?

multiciliated ependymal cells

what are the subdivided primary ependymal cell responses to aging

1. cilia dysfunction

2. ependymagliosis

3. beta-amyloid and parvalbumin buildup

4. periventicular white matter abnormalties

5. decreased V-SVZ neurogenesis

what are the two different cilia

green cilia - functional

red cilia - dysfunctional

satellite cells are derived from

embryonic neural crest

the satellite cells form

thin glial layer around each other perikaryon in the PNS ganglia

the central nervous system is composed of

cerebrum, cerebellum, and spinal cord

what can be found in the central nervous system (2)

1. white matter

2. grey matter

white matter is

presence of myelinated axons and myelin producing oligodendrocytes

grey matter is

abundant perikaryon, dendrites, astrocytes, and microglial cells

purkinje cells are in the

cerebellum

pyramidal cells are in

cerebrum

layers of the cerebral cortex - gray matter

1. molecular layer - outermost layer

2. outer granule layer - granule cells

3. outer pyramidal layer - small pyramidal cells

4. inner granular layer - axonal ramification of afferent fibers

5. inner pyramidal layer - large pyramidal cells

6. layer of pleiomorphic cells - white matter

peripheral nervous system is composed of

cranial, spinal, and peripheral nervers

what can be found in CNS nerves that are also in the peripheral nervous system composition

1. ganglia

2. myelinated nerve endings

peripheral nerves are subdived into

1. sensory

2. motor

sensory neurons

a single neuron connnecting the sensory ganglion sensor to the spinal cord / brain stem

somatic neurons are either

somatic afferents or visceral afferents

motor neurons are

somatic efferents

the connective tissue of the PNS holds

1. peripheral nerves

2. Schwaan cells

what are three components of the connective tissues of PNS

1. endoneurim

2. perineurim

3. epineurium

endoneurim

loose connective tissue, 90% Schwaan cells - 10% macrophages, mast cells, and fibroblasts (rare), fascicle

perineum

specialized connective tissue, metabolically active diffussion barrier that helps form the blood nerve barrier which helps maintain nerve ionic homeostasis, composed of contractile squamos cells

epineurium

dense irregular connective tissue, surrounds fascicles, have adipose tissue by larger nerves